This invention generally relates to filters in HVAC systems. More particularly, embodiments of this invention relate to techniques for estimating filter status, estimating HVAC characteristics, and sensors relating to filters in HVAC systems.
Many HVAC systems utilize a filter for cleaning the air, which is heated or cooled by the HVAC system. In the case of residential and/or light industrial buildings, these filters require cleaning or replacement, usually by the occupants, after a period of use. A dirty filter restricts airflow through the HVAC unit, which inhibits the HVAC system's ability to force air through the ductwork and interchange the air in the building. Often, replacement of the filter is neglected by the user, and the performance of the system consequentially degrades. When the performance of the system degrades, not only dues the system become less effective in terms of the time needed to raise or lower the temperature—leading to less comfort for the occupants, the degraded performance can also be also a significant source of wasted energy resources and money. Thus, it is desirable to have an indication of HVAC filter status, and in particular an indication of when the HVAC filter is sufficiently clogged that it should be cleaned or replaced.
Various attempts have been discussed at determining HVAC filter status. For example, U.S. Patent Application Publication No. 2007/0228183 discusses the determination of a clogged filter via airflow sensors located in various locations. A number of techniques rely on fan motor speed monitoring. For example, U.S. Patent Application Publication No. 2007/0234746 discusses comparing a historical calculated airflow restriction with a current as a possible indicator of a clogged filter. The airflow restriction is calculated using a static pressure drop, which can be calculated as a function of delivered airflow, and from sensed fan motor speed. U.S. Pat. No. 6,003,414 discusses detecting a clogged filter using static pressure, which can be derived as a function of delivered air flow and sensing the fan motor speed. U.S. Pat. No. 7,261,762 discusses detecting a clogged filter based on system resistance determined using fan speed and power. Finally, U.S. Pat. No. 7,188,482 discusses detecting faults, including filter plugging, in a duct free heat pump system known as a multi-modular split system (MMS) by utilizing various sensors located within the heating system.
Another problem that sometime arises is during installation and/or setup of a new thermostat, the HVAC system capacity may not be known by the installer or building occupant in the case of residential and/or light industrial buildings. Thus it is desirable to provide a technique of estimating HVAC system capacity from other available information.